Compression rate, how much?

[Jesse/DVK]

Goodevening guys,

I would like to know more about compression rate, I know the cam has a lot to do with it. But how high can you go with todays gas? Here in the Netherlands we have 95 and 98 octane.

I'm building an 1915 with a W120. My heads are 43cc's, I calculated that with 1mm deckheight I have a CR of 10.5:1 and with 1,5mm 10:1. Is this too much?

Thanks

Jesse

[Rasser]

I would change to a w130 cam and go for 1mm deckheight, then your c/r is just right - seriously i would!

[Jesse/DVK]

Isn't that too wild for the street? Will be running 40 DRLA's. Heads are ported 041 with 39x35.5 with single springs. Need to swap them for dual for the W130 I guess.

[GreenTom]

Hi,

You should put dual springs with w120 also.
with the CR if youre sure with qualiy of youre fuel and acuracy of the timing setings go for 10,5:1 and some FK7 and 1,4rockers (bug Packs are really not so bad for that price).
when I was driving through nederlands with my bug I was buying gas on Aral mostly (as I remember) - not so bad fuel.

[Jesse/DVK]

Well the heads have Remmele springs and they should be good with a W120 because they are very strong.

Listening to you guys I have two options, W120 with 10:1 or W130 with 10.5:1, around how much HP will they differ? And how drivable are they?

(I'm using the stock rockers on HD shaft)

Jesse

[Torben Alstrup]

IMHO 10-1 on a W120 cam is too much. You will heat up the heads fast when you hit the freeway. And you will experience detonation problems, even on 98 octane fuel.
I agree with Rasser that you should go up in cam or reduce the CR. If you think a W130 is to hot for your taste, go for a W125 or a Web 121/125 (Which I personally like better) and of course dual springs.

The Remmele HD springs are good, but not that good. If you use them in a set up like what you menthioned, along with a set of titanium retainers and CB 78 gr. lifters,  you can get by if you limit the rpm to 6300 max 6500. And that´s the limit, period!
T

[rebel]

Well, I have a similar setup, but not that hot.

It's 1915cc with 040 heads modified to 40x37.5, scat C35 cam (similar to w110),1.1:1 rockers on solid shafts, all topped up with a pair of DRLA 40s. The CR is set to about 9.2:1.
Engine is definitely not a racing type, but very, very streetable and fast enough for me (at this stage of hobby).

[Bewitched666]

Jesse,

use shims till you get the cr about 9.5 or 9.0 for the W120 or w125.How much is your case decked btw?
W130 is to much of a cam unless your heads flow alot and you will use IDA's or some bigger carb then 40 dells

Gr,
Stanford

[alex d]

I would open the chambers to gain some ccs

[Jesse/DVK]

IMHO 10-1 on a W120 cam is too much. You will heat up the heads fast when you hit the freeway. And you will experience detonation problems, even on 98 octane fuel.
I agree with Rasser that you should go up in cam or reduce the CR. If you think a W130 is to hot for your taste, go for a W125 or a Web 121/125 (Which I personally like better) and of course dual springs.

The Remmele HD springs are good, but not that good. If you use them in a set up like what you menthioned, along with a set of titanium retainers and CB 78 gr. lifters,  you can get by if you limit the rpm to 6300 max 6500. And that´s the limit, period!
T

I don't mind going with dual springs, how extreme is a 1915 with a W130? It's not being used as a daily driver but more of a weekend stoplight racer . But won't the DRLA's be to small for a W130, W125, Web 121/125?

Jesse

[Rasser]

Well the heads have Remmele springs and they should be good with a W120 because they are very strong.

Listening to you guys I have two options, W120 with 10:1 or W130 with 10.5:1, around how much HP will they differ? And how drivable are they?

(I'm using the stock rockers on HD shaft)

Jesse

When i built my 1914 engine first time, it was with a w120 and remmele springs just as yours. And I ended up needing a new valve/seat job, and having heads machined for dual springs. DON´T run a w120 with single springs. Off course it depends on how much your heads flow too. My heads were heavily ported 040 heads with 40-37,5mm valves.

I later changed to a w130 cam and 1,25 rockers (WAAAY to hard on the valvetrain - but lot´s of power). Engine made 147 HP with 40mm dells, and was easy to drive.

Looking back... I should have bought a set of 48 IDAs insteadof the dellortos, 48´s can grow with the engine and they have THE look ;-)

Why not go for a FK8 cam, 1.4 rockers and dual springs - That is a superb allround cam that isn´t so hard on the valvetrain.



Here is two videos of my car with the w130cam and 40mm dells (37venturis)

<a href="http://video.google.com/googleplayer.swf?docId=-5782694275058868534" target="_blank">http://video.google.com/googleplayer.swf?docId=-5782694275058868534</a>
<a href="http://www.youtube.com/v/HwaK8WF9oWM" target="_blank">http://www.youtube.com/v/HwaK8WF9oWM</a>

[Jesse/DVK]

Well I can buy 1.4 bugpack rockers from a friend so an FK-8 is also a good option.

Damn, it's quite hard to choose, there are a lot of options .

[Bewitched666]

But still keep your cr ratio between 9-9.5 Jesse

[Jim Ratto]

40DRLAs are too small, with that much overlap for that cylinder cc.
What's the largest diameter venturi for the 40DRLA? 34mm?
to flow enough air to utilize that 130 cam, you'd need 37-38mm venturi.

[Rasser]

40DRLAs are too small, with that much overlap for that cylinder cc.
What's the largest diameter venturi for the 40DRLA? 34mm?
to flow enough air to utilize that 130 cam, you'd need 37-38mm venturi.

36 is largest size stock for 40mm (if I remember correctly) - I had 37mm vents custom made for mine. Too small ?... maybe, but still pulled almost 150hp

[Jim Ratto]

40DRLAs are too small, with that much overlap for that cylinder cc.
What's the largest diameter venturi for the 40DRLA? 34mm?
to flow enough air to utilize that 130 cam, you'd need 37-38mm venturi.

36 is largest size stock for 40mm (if I remember correctly) - I had 37mm vents custom made for mine. Too small ?... maybe, but still pulled almost 150hp

peak power made @ 6800-7000 needs 37-39mm

[Torben Alstrup]

40 Dells are heavily underrated by peoples general opinion. Rasser went to the limit or thereabouts with his set up, and still being a street car. But 40 Dells will easily keep u with a 130 cam. FK8 is also an option.

I frequently build 2110´s with 40 Dells and pull 140 to just about 150 hp. No sweat. (Personally I do not like to go above 36 mm venturies, because of tuneability. Even 36és can be difficult) But when properly adjusted, the throttle response is incredible. Even motorcycle people lift an eyebrowe or two on a regular basis.
- Admitted, that they might pull 5-10 hp more with 44´s or IDA´s, but were talking street engines and very good driveability.
T
And Jim, even a W130 wohnt peak that high, unless you use radical heads and accepts to loose driveability under 3 grand rpm. they typically peak at about 6300.
And DO NOT just lower your CR with extra deckheight. Modify your chamber instead. Large decks create more heat, less clean and efficient burn and more pollution.

[Jesse/DVK]

<a href="http://www.youtube.com/v/HwaK8WF9oWM" target="_blank">http://www.youtube.com/v/HwaK8WF9oWM</a>

How cool! I watched that vid before I even had a bug a couple of years ago, from then on I wanted a bug and one with that engine! Cool to see i'm now building a similar engine 

So if I go with a FK-8, dual spring from I think GB? Should I then go for 10:1 CR of 10.5:1? Or something in between?

[Torben Alstrup]

I would consider 10,5 - 1 being max. and would personally aim for 10 to 10,3 - 1.
T

[Jesse/DVK]

Thanks guys, this is such a cool forum with all the info from you guys. Going for the 1915, K8, 10:1 combo.

[dirk zeyen]

in the CSP-shop they say you can use single springs with a W120 cam, they sell the scat single springs

dirk zeyen

[Torben Alstrup]

in the CSP-shop they say you can use single springs with a W120 cam, they sell the scat single springs

dirk zeyen

If you drive as hard as Rasser does, YOU CANT !  But if you follow my instructions menthioned further up, you can. But its the absolute limit. If you like to rev it to the edge 3 times a day, I would definitely go with duals.
T

[Rasser]

in the CSP-shop they say you can use single springs with a W120 cam, they sell the scat single springs

dirk zeyen

If you drive as hard as Rasser does, YOU CANT !  But if you follow my instructions menthioned further up, you can. But its the absolute limit. If you like to rev it to the edge 3 times a day, I would definitely go with duals.
T

Yeah - what Torben said!   

If you have an engine that can rev high and still make usable power, then it´s just stupid to limit the engine. Whats the fun in that ?

With my w130 and 1.25:1 combo I ended up using JPM dual springs - worked perfect!  (the actual lift was higher than 1.25:1 (scat), since my actual measured valve lift was 14.14mm, and it requires some serious valvespring-pressure because of the extreme acceleration the valves get with this combo)
This engine was LOADS of fun, but high strung!

If I remeber right, the valves started to float at around 6200-6300rpm (with the W120 cam). I know this because the retainer/clips started hitting the valveguides and you could hear this!!! (springside of the valveguides were not machined down like they should have been). This "spring-mistake" ended up costing me a new valve/seat-job, machining for dual springs and then offcourse new springs etc.

On a side note my W130 version of the engine made max hp at around 6600-6700 rpm (dyno), after 6600-6700rpm  the powercurve flatted out, but still continued making the same power a bit further - maybe this engine could have made more hp with a set of bigger carbs (this was an estimated guess by the dyno owner/operator)

[Jon]

I Norway there is a racing (<- stretching it) class called "Carcross", they refer to compression in millimeters..  like "2mm of compression" 

I get some of the same feelings from this discussion... one spring or two springs? Are all installation depths the same? Are all springs the same?
Or is it a given fact that you shim it up to 1,5 mm from coil bind always? It feels like apples and oranges... to me at least 
Wouldn't it be of bigger interest to discuss how much spring pressure the cam/rpm/valve/rocker require?

[Rasser]

I Norway there is a racing (<- stretching it) class called "Carcross", they refer to compression in millimeters..  like "2mm of compression" 

I get some of the same feelings from this discussion... one spring or two springs? Are all installation depths the same? Are all springs the same?
Or is it a given fact that you shim it up to 1,5 mm from coil bind always? It feels like apples and oranges... to me at least 
Wouldn't it be of bigger interest to discuss how much spring pressure the cam/rpm/valve/rocker require?

In my particular instance it´s hard to say I did it this way or the the other way, and it may sound confusing at times, talking about single/dual springs and different cams and compression rates. It´s because I build the same engine 3 times! :-), I changed  cam, compression, headwork, rockers, springs etc.  3 times with the "same" engine.

And yes with the w120 (1. version of the engine), the Remmele valve installationheight were shimmed according to bergs technical book (38,4mm - if i remember correctly).
On the w130-1.25:1 version I had to do some "adjustments", since I couldn´t get enough clearance before coilbind if I shimmed the springs according to Bergs. I then set the springs up with only coilbind clearance in mind, and not paying much attention to spring install height. I personally think 1,5mm clearance is FOR RACING USE ONLY  (I have experienced GB273A dual springs to break after only a couple 1000´s km with this little coil bind clearance). I aim for 2,5mm clearance for a street engine, and thats the way I build my engines now. But if it was meant for racing ONLY, I would go for 1.5mm if I needed the extra bit of spring-pressure.

I totally agree with you that it is easier to say what spring pressure a certain combo requires. BUT with that beeing said, I can´t see the harm in telling someone that a W series cam requires more spring pressure than an equivelant FK cam because of the "valve"-acceleration. I think that is what both Torben and me tried to point out. Sorry for not beeing clearer.

Another thing is there are so many variables: steel/alu pushrods, alu/ti/steel retainers, lifter weight, valveweight, ACTUAL rocker ratio, and then offcourse the cam choice!
I think it´s very hard to make a list of parts, and then do the math and come up with the spring pressure needed. This is were others experince and knowledge come in handy - and since the bearth of vwforums on the internet, this has fortunately become MUCH easier.

But as with everything you learn from someone elses mistakes, and I don´t think theres anything wrong with this.
Not all springs you measure have the advertised spring pressure, and then it´s nice to know what works for others in a particular combo and what doesn´t, and then make your choice of springs from this.

[Jon]

I can´t see the harm in telling someone that a W series cam requires more spring pressure than an equivelant FK cam because of the "valve"-acceleration. I think that is what both Torben and me tried to point out. Sorry for not beeing clearer.

There is absolutely no harm in letting people know about how cams that make great low end power expose the valves to hefty acceleration.
As most people think that dubble springs is a race only thing, when its actually required for the street cams to.

My hope were more in the lines of seeing some pressure figures , so people can self decide how they want to achieve that.

You both have very valuable inputs in this field... thanks!

[dirk zeyen]

thanks for information!!!
my 2007ccm engine with stock size valves, 45 drla revs not more than 6000rpm. so the single valvesprings are fine.
i think to much valve pressure kills power, so not more than needed.

about the w130 cam, i'm with jim ratto, look at dave rhoads engine w130cam 40/35.5 valves 82X88 max power at 7000rpm

dirk zeyen

[Jon]

thanks for information!!!
my 2007ccm engine with stock size valves, 45 drla revs not more than 6000rpm. so the single valvesprings are fine.
i think to much valve pressure kills power, so not more than needed.
dirk zeyen

Rpm in not the only thing defining the need for spring pressure.
How much spring pressure is enough is the big question...
To much kills HP...true, but it's when you learn what too little does that you start thinking...
We all makes our choices.

[dirk zeyen]

hello,

my engine is more than 10 years old and it works
scat lifters
scat single valve springs
crmo pushrods
78 scat crank
p/c 90.5
45 dells
stock size valves in ported heads
w120 cam

with a 4.375 r/p and 0.93 4th 195/65-15 it is fun on the street

dirk zeyen

[Jim Ratto]

hello,

my engine is more than 10 years old and it works
scat lifters
scat single valve springs
crmo pushrods
78 scat crank
p/c 90.5
45 dells
stock size valves in ported heads
w120 cam

with a 4.375 r/p and 0.93 4th 195/65-15 it is fun on the street

dirk zeyen

you've got nice light, small valves. I bet if you disassembled your heads, you "might" find that your keeper grooves are starting to burr up and you might find an edge around under side of retainers where keepers sit. Springs most probably dead.
I think Engle 120 is probably on the fence depending on state of tune of engine, how it is driven, how heads were assembled, and quality of springs. I used single springs only in Kyle Madden's engine, and taht was so long ago now, I don't remember the cam. I think it was C25 or C35 Scat. It was a moderate profile, which was perfect for his motor and his driving/expectations. I knew he was going to gentle on the motor, and just wanted a cruiser, not a race car.
My first stroker ran an Engle 125 with 40 x 35.5 and single HD springs. Blasphemy, right? I never heard the valves float, but again, I didn't build this to race, even on the street. It was my first step into bigger motors and I only wanted to get my toes wet really. I only ran it up to 6000-6200, as it was used more as a freeway motor, which it handled well. However, about 7 months later, I switched heads and upon disassembling them, found the springs dead, keeper grooves burred up (you'll realize this when you try to get valves out of heads and they hang up in guides!), retainers showed wear, ends of springs were worn shiny and valve job had gone to hell.
My dad's truck engine was 94 x 74 with small Scat cam and Denham 40 x 37 heads and ran in his '59 Truck, with stock gears and reduction boxes. Because it would get rpm so fast, we put dual springs since acceleration rate was severe.
Hope this perspective helps.